Fast app reinstall: Add video in the app downloading screen

Bug: 835029
Change-Id: Ie39c2ab0956f01ce51bdf1e2fa0e8de30de51160
Reviewed-on: https://chromium-review.googlesource.com/1144272Reviewed-by: Wenzhao (Colin) Zang <wzang@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Yue Cen <rsgingerrs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583470}

chrome/browser/resources/chromeos/login/app_downloading.css

@@ -17,3 +17,8 @@
 #app-downloading-video-container {
   margin: 80px auto auto;
 }
+
+#app-downloading-video-container video {
+  height: 204px;
+  width: 230px;
+}

chrome/browser/resources/chromeos/login/app_downloading.html

@@ -22,7 +22,13 @@
         [[i18nDynamic(locale, 'appDownloadingScreenDescription')]]
       </div>
       <div id="app-downloading-video-container" slot="footer">
-        <!-- TODO(rsgingerrs): add the app downloading video -->
+        <if expr="chromeos and _google_chrome">
+          <video loop="loop" autoplay="autoplay" muted>
+            <source
+                src="../../../internal/resources/arc_support/videos/app_downloading.mp4"
+                type="video/mp4">
+          </video>
+        </if>
       </div>
       <div slot="bottom-buttons" class="layout horizontal end-justified">
         <oobe-next-button id="app-downloading-continue-setup-button"